The corset is actually really rare. It's great that you can now get it for free :)
If you're from Poland:
1.) Make sure you are logged into Stardoll.
2.) Click here.
3.) Once the page has loaded, it should be in your suite.
If you're not from Poland:
2.) Go to http://www.stardoll.com/en/ with the proxy, then log in.
3.) Once you have logged in, go to these contest links:
CROP SWEARTER: http://www.stardoll.com/en/contest.finish.php?id=1076
4.) Once the page has loaded, close the proxy. They should be in your suite.